NEW WOOD STUD WALL TO EXISTING CMU WALL - VERTICAL CONNECTION??

[jpw2913]

I'm trying to help a contractor with a residential remodel. The existing house has a 9'-0" high 8" cmu block exterior wall (reinforcing unknown at this time). They want to add to the wall height with 2x6 wood studs to make this a 2 story house. The trick here is that in a certain area of the house, there is no floor that will be framed to the block/wood wall connection. So I'm trying to determine if there is a connection that will take care of the "hinge point" where the wood wall meets the block wall. A Simpson MSTC strap will help take care of the uplift (along with anchoring the sill plate to the top of the block wall), but what about the hinge where the two walls connect? Any thoughts? I've attached a sketch of the wall section.

Thanks for any help.

 

[XR250]

Nothing off the shelf that I can think of. Even so, the wall would be flimsy with 2x6's as the upper half given its 18 ft. height. Is there a way to add a flat steel plate or channel or multiple wood 2x8's the top of the CMU to act as a horizontally spanning girt that would react against the bordering floor system?

 

[KootK]

I agree with XR250 on this one. What you need is a girt rather than a moment connection between the block and the stud wall. Over what length is the top of the block wall unbraced by the floor? For something on the order of a stair well condition, the block wall itself might be able to perform the girt function.

 

[EcoGen]

A bond beam at the top of the CMU wall could act as your girt. But you would need to check it against its span. Which would be the horizontal unbraced length of the wall. I know you want to have an open floor at this location. But you could consider adding horizontal beam or beams perpendicular to the wall to brace it.

I imagine the tension strap you mentioned also helps some in minimizing hinge rotation at this joint.